When the axes of rotation of a driving and a driven shaft are not in alignment, there are a number of possible categories of such misalignment. One may be considered parallel offset, that is, where the axes are parallel to each other but spaced from one another in a transaxial direction. Another may be considered angular offset, which is where the axes are not parallel but intersect at an angle, although the axes may lie in parallel planes. The third is misalignment in the axial direction.
Numerous coupling devices have been developed to transmit power from or between two such shafts. U.S. Pat. No. 3,625,024 to Kikuchi, which issued Dec. 7, 1971, and U.S. Pat. No. 4,321,805, which issued to Bossler, Jr. (hereinafter Bossler) on Mar. 30, 1982, disclose flexible disc couplers. In disc couplers, a flexible coupling device connects through attachment points on the coupling device to driving and driven elements of a drive train, such as rotatable shafts or hubs on such shafts, at the same radius from the center of the coupler device. Disc couplers further can be divided into closed and open arm types.
Closed disc couplings always carry torque load in tension between the attachment points of the coupling device. Closed discs, such as the Formsprag.RTM. type (Formsprag.RTM. is a registered trademark of Dana Corporation), are also well known, offer high torque transmission, but are not capable of handling severe misalignments of driving and driven shafts. Also, in prior art disc couplings, the phenomenon of "fretting" occurs. There are two types of "fretting", namely (a) nutating fretting, such as is caused by movement around a bolt bearing washer, and (b) linear fretting which occurs by the rubbing together of one disc on another away from the connection area of the disc and which generates a shearing action. As the disc material rubs, it oxidizes and disturbs the substrate, eventually propagating a fatigue crack. This is especially prevalent in prior art discs having a thickness on the order of 0.015" to 0.090". Coating on such discs may extend their life, but they also deteriorate under the rubbing action.
In contrast, open arm disc couplings carry the torque load in compression or tension depending on the direction of rotation of the coupling device. Bossler is an example of the open arm type of coupling device. Such prior art open arm disc coupling devices are limited in their torque carrying capabilities. This is true in Bossler, for example, because the arms of the Bossler coupling used to transmit torque are long and are subject to column buckling. The four Bossler arms are formed into two Vs with a single beam or column connecting the vertices of the two Vs. The column which connects the "V", is susceptible to buckling under high torque loadings. This also limits torque carrying capability.
Another type of coupling provided to transfer loads to accommodate axial misalignment or displacement between a driving and a driven shaft or displacement between a driving and a driven shaft is found in a series of the following patents: U.S. Pat. Nos. 4,282,723; 4,317,339 and 4,331,004, which issued on Aug. 11, 1981, Mar. 2, 1982 and May 25, 1982, respectively, to Richard Schmidt.
In the Schmidt devices, the actual coupling element, which is attached to each of a driving and a driven member, includes an annular portion and two pairs of parallel arms. Whereas the arms themselves are parallel, the pairs are not symmetrical. The arms are sufficiently flexible to provide good axial and/or angular displacement to compensate for the misalignment. However, there are inherent limitations in the design resulting in a limited ability to transfer high torque loads. This results from the fact that, regardless of the direction of rotation, at least one pair of arms at all times is in compression without any compensating tensile component. The result is that, under high torque conditions, the arm under compression is susceptible to buckling which, therefore, limits the load carrying capacity of the entire coupling element. The Schmidt type of device is also known as an open-end arm or open-link type of coupling.
Diaphragm-type coupling devices are known which permit large torque transmission, but are able only to handle slight angular misalignment on the order of 1/4 degree to 1/3 degree. In diaphragm-type coupling devices, either the driving or driven shaft connection is located proximate the center of the coupling device at an inner radius, and the other connection of the driving or driven shafts is located at an outer radius. Torque load is carried between the two shafts by the coupling device through a coupler to connection points which are attached to either one of the shafts. The torque load is carried in shear between the two radii of the connection points through a membrane. An example of this diaphragm-type of coupling device is U.S. Pat. No. 4,776,824, which issued to Barth on Oct. 11, 1988. The Barth diaphragm-type coupling device has circumferentially-resilient spring leaves which are not rigid in the circumferential direction, but rather are designed to flex between the contact surfaces of the disc-like membrane in the circumferential direction. The Barth type coupling device is unable to carry a significant amount of torque load in shear across the spring leaves because the spring leaves are not rigid in the circumferential direction and, under a high torque load, would shear off near the thin portion of the spring leaves.
Another example of this diaphragm-type of coupling device is U.S. Pat. No. 2,386,017, which issued to Venditty on Oct. 2, 1945. The Venditty diaphragm-type coupling device has spokes which connect each transverse corrugated foot or cross piece such that they are not substantially proximate a hub portion. Due to the radial length of the spokes, the spokes would not be rigid when carrying a torque load. Instead, the spokes would flex circumferentially from the torque load. The Venditty coupling device operates in a diaphragm type configuration by connecting all of the cross pieces at one radius to either the driving or driven element of a drive train and by connecting the hub portion of another radius to the other of the driving or driven element which is not connected to the cross pieces. The Venditty coupling device completely embeds the corrugated feet or cross pieces in a single rubber ring and connects the rubber ring to either the driving or driven member.
Yet another example of this diaphragm-type of coupling device is U.S. Pat. No. 2,046,208, which issued to Paulsen et al. on Jun. 30, 1936. The Paulsen et al. diaphragm-type coupling device has openings proximate annular portions which connect a central flat portion to an outer rim portion. The openings are in the outer rim portion at an outer radius of the disc and are connected to the one of the two elements of a drive train (i.e., driving and driven elements). In addition, fixing means are located in the central flat portion at an inner radius of the disc and are connected to the other one of the two elements of the drive train.
It is an object of the present invention to provide a coupling mechanism which is capable of transferring torque loads in shear in addition to either tension or compression alone, to approximate a diaphragm-type performance, while permitting higher angular misalignment, and axial displacement, both continuous and intermittent.
It is another object of the present invention to provide a coupling mechanism which is capable of offsetting compression loads in each torque transmitting member by a tension load.
It is another object of the present invention to provide a coupling which eliminates fretting effects and fatigue adjacent to the means of attachment.
It is another object of the present invention to provide a coupling mechanism which is capable of removing flexible members without removing coupling hubs, intermediate members or floating shafts regardless of the coupling design.
It is another object of the present invention to provide a coupling mechanism which is capable of achieving increasing levels of critical speeds and reducing the torque stress.
It is another object of the present invention to provide a coupling mechanism which is capable of inhibiting fretting corrosion fatigue through unidirectional torque loading techniques.
It is another object of the present invention to provide a coupling mechanism which is capable of having an increased critical speed through unidirectional torque loading in the direction that subtracts centrifugal loading.